Safety lock for band saw tensioning mechanism



1953 R. L. CRANE 2,644,492

SAFETY LOCK FOR BAND SAW TENSIONING MECHANISM Filed June 21 1950 3 Sheets-Sheet l SAFETY LQCK FOR BAND SAW TENSIONING MECHANISM Filed June 21, 1950 R. L. CRANE July 7, 1953 3 Sheets-Sheet 2 faawil, 9W

July 7, 1953 R. L. CRANE SAFETY LOCK FOR BAND SAW TENSIONING MECHANISM Filed June21, 1950 5 Sheets-Sheet 3 Patented July 7, 19 53 SAFETY LOOK FOR BAND SAW TENSIONING MECHANISM Robert L. Crane, Savage, Minn., assignor to Continental Machines, Incorporated, Savage, Minn, a corporation of Minnesota Application June 21, 1950, Serial No. 169,501

6 Claims. (01.143- 27) My invention relates generally to machine tools of the type utilizing a cutting band such as band saws or the like, and more specifically to mechanism in machine tools of this type for maintaining a desired minimum of tension on the cutting band.

In band saws of the type wherein cutting band tension is maintained by shifting one of the pulleys over which the cutting band is trained, and particularly when the pulley is shifted by means of fiuid pressure operated mechanism, there is frequently a tendency for the shiftable pulley to move in a direction relieving tension on the band when the machine is at rest. Then when the machine is again put into operation, the cuttin band is so loosely engaged by the pulley over which it runs that it fails to track properly thereon and runs off the pulley before sufficient tension is applied thereto. When this occurs,

the band is frequently damaged and possibledanger to the operator results. The primary object of my invention is, therefore, the provision of means for preventing undue release of tension of the cutting band in machines of this type when the machine i in an inoperative condition.

Another object of my invention is the provision of means vfor preventing release of tension of the cutting band .for an indefinite period of time.

Another object of my invention is the provision of brake mechanismassociated with the mounting means for the shiftable pulley and normally set inbraking engagement to arrest shifting vision of means for locking the shiftable'p ulley mounting against band tension releasing movement, which is simple and inexpensive to produce, which is rugged in construction, and which a is efiicient in operation and durable in use.

Other highly important objects and advantages of my invention will'become apparent from the following detailed specification, appended claims, and attached drawings.

Referring to the drawings, which illustrate the invention, and wherein like characters indicate like parts throughout the several views:

Fig. 1 is a view in front elevation of a sawin machine band made in accordance with my invention;

Fig. 2 is an enlarged vertical section taken on the line 2-2 of Fig. 1;

Fig. 3 is a fragmentary detail partly in front elevation and partly in section taken substantially on the line 3-3 of Fig. 2; A

Fig. 4 is an enlarged axial section of one of the brake elements of my invention taken sub stantially on the line 44 of Fig. 3; and

Fig. '5 is a diagrammatic view illustrating, fluid pressure system of my invention. j

Referring with greater detail to the drawings, a band saw machine is indicated in its entirety by the numeral I, the fixed frame structure'of which comprises a base 2, a generally vertical column 3 and a head 4. The head 4 proJ'QQts laterally outwardly from the upper end of the column 3 overlying a laterally projected portion of the base 2 to define therebetween a throat or working space in which is disposed a work-supporting table 5 mounted on the extended end portion of the base 2. A drive wheel 6 is mounted on the base 2 below the table 5, and an idler wheel or pulley l is mounted for rotation in the head 5 in tandem relationship to the drive wheel 6. An endless cutting band 8, in the nature of a band saw or the like, is trained'over the wheels 6 and land through a slot 5 in the work'tablej, and guided by guide rollers ll! of a saw guide ll secured to the head it by means or" a supporting post 42. The drive wheel 6 is mounted fast on a shaft it, which is driven from a drive motor M, by means of V-belts l5 and I6, indicated by dottedlines in Figs. 1 and 5, a conventional vari able speed pulley IT and suitable transmission a pulley ii, the belts I5 and i6, and transmissionmechanism, not shown, but contained within the base 2. The variable speed pulley H is journalled to a mounting bracket I8 pivotally secured to the base- 2, as indicated at I9. The variable speed detailed showing and description thereof istherefore unnecessary.

The idler pulley l is mounted fast on the outer A end of a shaft '2t,'which is journalled in floating bearing bracket 2! by means of anti-friction bearings 22. The bearing bracket 2! is pivotally mounted on a shaft 24 extending transversely of a mounting member 25 which is mounted for vertical sliding movement on a fixed plate 26 rigidly secured to a. wall section 2': of the head 4 by nut-equipped bolts or the like 28. The bearing bracket 2| is provided with an upstanding lug 2 9,

which forms the base of support for one end of a compression sprin 35 interposed. therebetween and the upper end portion of the mounting member 25, whereby to bias the bearing bracket H in one direction of pivotal movement about the axis of the shaft 24. A depending ear 3! integrally formed with the bearing bracket 2i is adapted to have abutting engagement with one end of a push rod 32 axially slidable in a laterally extended boss 33 integrally formed with the mounting member at its lower end portion. The push rod 32 is adapted to be moved by an adjustment knob or handle wheel rigidly mounted on a vertical shaft 35 journalled in the bottom portion of the head 4. The upper end of the shaft 35 is cross-sectionally polygonal, as indicated at 35 and has telescoping engagement with the lower end of a sleeve the upper end of which telescopes over the lower end 38 of a screw threaded shaft 39. Ihe shaft 39 has screw threaded engagement with a threaded portion of a bracket Ml integrally formed with the boss 33, and engages one side of a block-like lever M pivotally mounted on the bracket 49. A portion of the lever 4| engages the projecting end of the push rod 32 and is adapted to move the push rod upon rotation of the knob 34 in one direction against bias of the compression spring 3! Rotation of the knob 34 in the opposite direction will cause the idler wheel 1 to be tilted in the oppo- 1 site direction. It should be noted that when the cutting band .3 is mounted on the wheels 6 and l, tension of the cutting band 8 will be added to the bias of the spring 38 to cause the depending ear 3! to bear against the adjacent end of the push rod 32. This load is transferred through the lever 4! to the screw 39 and the bracket portion in all positions of the mounting member 25 with respect to the plate 28. By reference to Fig. 2, it will be seen that the telescopic sliding relationship between the lower end 36 of the screw 38 and the sleeve 3? permits free vertical movement of the screw 39 and associated parts with respect to the knob 34.

For the purpose of raising and lowering the idler wheel 1 and mounting member 25 therefor with respect to the drive wheel 5 to make possible the application of the cutting band 8 to the wheels 6 and I and apply proper tension to the cutting band 8, I provide a fluid pressure motor in the nature of a fluid pressure actuator cylinder 42 and a cooperating piston .3. The piston 43 depends from the lower end of the mounting plate 26 and is securely held by means of screws or the like 44. end rigidly secured to the piston 43, and extends upwardly through the upper end of the cvlir jgr 42, having its upper end mounted fast on the lower end portion 45 of the mounting member 25.

Fluid under pressure is supplied selectively to opposite ends of the cylinder 4?. from a supply tank 4'! by a pump d8 driven from the motor it through the medium of a V-belt 49 running over suitable pulleys on the motor and pump. The pump 48 is interposed in a fluid pressure conduit 50 which extends to a check valve 5! in a valve block 52. A passage 53 in the valve block d2 extends from the check valve 5! to a valve chamber 54 in which is mounted a directional valve element 55. A pair of conduits 53 and 5'! extend from the valve chamber 54 to the lower and upper ends respectively of the cylinder 42. As shown in Fig. 5, the valve element 55 is formed to provide circumferentially spaced axially extending faces or sides 53, 59, and 88, which cooperate with the A plunger rod 45 has its lower circular wall of the chamber to define respective circumferentially spaced valve compartments 58, 59', and Gil. The valve element 55 is further provided adjacent one end with a transverse passage 61 extending from the face 58 to the side of the element 55 between the faces 59 and 60. A second passage K32 extends axially inwardly from the opposite end of the valve element 55 terminating short of the transverse passage BI and has comm nication with a pair of passages 63 which extend radially inwardly one each from one of the faces 59 and til. A passage 54 in the valve block 52 communicates with the passage 62 and has connection with a fluid return conduit 65 leading therefrom to the supply tank Al. As shown, a pressure relief valve 58 has connection with the fluid pressure conduit 50 as indicated at 67, and with the return conduit 65 as at 68.

Manipulation of the valve element 55 by means of its handle 55 (see Fig. l) to the position thereof shown in Fig. 5 permits fluid to be forced under pressure from the supply tank all through the pressure conduit Eil, the passage 5-3 leading proper tensioning pressure to bands of difierent widths, I provide an adjusting pressure regulator valve $3 in the valve block 52. As shown in Fig. 5, one side or" the pressure regulator valve 69 communicates with the passage 53 in the valve block 52 through a conduit it and a passage H. The opposite side of the valve 69 communicates with the fluid return conduit 65 by a passage 72 in the valve block 52 extending to the passage 64 therein. A conventional pressure gauge 13 is shown as being connected to the conduit 75 for indicating the exact pressure applied to the piston 43. Inasmuch as the pump 48 operates continually during operation of the machine and delivers a constant supply of'iluid, the greater part of the fluid supplied to the valve block 52 is by-passed through the pressure regulator valve 69 and returns to the supply tank il. During upward movements of the piston 43, fluid in the upper portion or" the cylinder t2 will be moved through the conduit 56 into the chamber 59 from whence it will flow through the passage 53 extending inwardly from the face 59 and passage 62 of the valve element 55 into passage G4 and return conduit 55 to the supply tank 4?. Move ment of the valve element 55 in a clockwise direction with respect to Fig. 5, sufiicient to effect communication through the passage 6i with the conduit 56, will cause fluid under pressure to be delivered through the conduit 55 to the upper portion of the cylinder 1-2 to cause downward movement of the piston 13 and subsequent loosening of tension of the cutting band 8.

Inasmuch as the pump 48 is dependent for its operation on the motor l4, shutting down of the motor M will shut off band tensioning pressure of fluid to the lower end portion of the cylinder 42. It should be noted however that the check valve 5| prevents immediate return of fiuid backwardly through the pump 38 from the lower end of the cylinder 42. However, when the machine has been idle for an appreciable length of time,

- to the next, this downward movement of the shiftable pulley mounting member 25 will frequently be suflicient to cause loosening in the cutting band to'a point where, when the machine is again put into operation, the band 8 will run off of the pulleys 6 and I and become tangled in the machine before the operator can render the same inoperative. To prevent this movement of the shiftable pulley l and the mounting member 25 therefor in a band tension releasing direction, I provide novel brake'means including cooperating brake elements M and 15, the former of which comprises a toothed rack 16 extending in the direction of movement of the pulley mounting member 25 and secured thereto by bolts or the like", and the latter of which comprises an extendable and retractable piston plunger' 19 'sl-idably mounted in and projecting outwardly from a bearing 19' of a fluid pressure cylinder 1'8 rigidly secured to the fixed wall section 21 of the machine. The plunger rod 19 isrigidly secured at its inner end to a piston Bil s'lidably mounted in the cylinder 18 and is disposed at an angle with respect to the rack 16 whereby the outer free end of the plunger rod 19 will engage one of the teeth of the rack 16 when the plungerrod I9 is in an extended position. The plunger rod 15 and piston 80 are normally urged toward braking engagement of the plunger 19 with the rack 16, to arrest downward movement of the shiftable pulley mounting member 25, by a coil compression spring 81 one end of which thrusts against the piston 80 and the other end of which engages the inner end of an adjustable abutment screw valve element 55.

- rendered inoperative and sufilcient leakage of 82 which is threaded into an end wall 83 of the cylinder 18. A look nut 84, screw threaded on the abutment screw 82, when tightened against the end wall 83 prevents accidental movement of the abutment screw 82. I further provide a stop screw 85 extending axially of the abutment screw '82 and operative to limit movement of the piston 80 and plunger rod 19 in a direction against bias of' the spring 8|. v

-The fluid motor piston 80 divides the cylinder 7 I8 into chambers 86 and 81, the former of which is a pressure chamber communicating with the pump 48 through a fluid conduit 88 one end of which is coupled to a passage 89 leading to the chamber 86 through theside wall of the cylinder 18, and the other end of which isconnected' to a conduit 1! y The chamber 81, in which iscbntained the spring 8i, communicates'with a conduit 90 through a passage 9| in the side wall of the cylinder 18, the conduit 96 being connected 65. It should be noted that the connection of the conduit 88 to the conduit 15 permits fluid under pressure to be introduced to the chamber 8B whenever the fluid pump is in operation and irrespective of the position of the directional fluid has occurred between the side wall of the cylinder 42 and the piston 43 therein to permit downward movement of the shiftable .pulley mounting member 25, the reduction of fluid pressure in the system permits the spring 8! to move the piston and plunger 13 outwardly into engagement of the outer end of the plunger rod 19 with one of the teeth of the rack 16 to arrest further downward movement of the shiftable pulley l and its mounting member 25. The pressure of the spring 8! may be adjusted by the indefinitely. Then, when the machine is again put into operation, fluid pressure set up in the system by the pump 48 simultaneously urges the piston 43 in an upward direction and the piston 86 in a brake releasing direction whereby the .shiftable pulley is again free for shifting move-' ments. Obviously, the pressure of the spring 8| is adjusted to exert slightly less pressure against the piston 80 in a brake setting direction than the minimum band tensioning pressure utilized under normal operating conditions of the machine, so that pressure of the spring 8| will be overcome immediately after the pump 48 has been put into operation and regardless of the band tensioning pressure used within a predeter- I mined pressure range.

My invention has been thoroughly tested and found to be completely satisfactory for the accomplishment of the above objects; and while I have shown and described a commercial embodiment of my novel structure, it will be understood that the same is capable of modification without departure from the spirit and scope of the invention as defined in the claims.

What I claim is: v

1. In a machine of the class described, afixed supporting structure, a plurality of pulleys, a cutting band trained over said pulleys, means mounting one of said pulleys for shifting movements toward and from the other pulley structure to effect tightening and loosening of the band, a normally set brake associated with the shiftable pulley mounting for arresting bandloosening movements. of the shiftable pulley, said brake comprising cooperating brake elements, structure mounting one of the brake elements on the fixed supporting structure and the other thereof on the shiftable pulley mounting means and guiding one thereof for movements toward and away from the other thereof, yielding means urging said movable brake element toward its cooperating brake element to set the brake, and releasable pressure means asso-' ciated with the brake and with said means mounting the shiftable pulley for urging the shiftable pulley mounting in a direction to tighten said band and'for simultaneously urging said movable brake element in a brake-releasing direction away from its cooperating brake element against bias of said yielding means, said yieldingmeans being responsive to release of said releasable pressure means to move said movable brake element toward brake setting engage ment with its cooperating brake element.

2- In :a machine of the class described, a fixed supporting structure, a plurality of pulleys, a

cutting band trained over said pulleys, means mounting one of said pulleys for shifting movements toward and from the other pulley structure to effect tightening and loosen ng of the band, a normally set brake associated with the shiftable pulley mounting for arresting bandloosening movements of the shiftable pulley, said brake comprising cooperating brake elements, structure mounting one of the brake elements on the fixed supporting structure and the other thereof on the shiftable pulley mounting means and guiding one thereof for movements toward and away from the other thereof, yielding means urging said movable brake element toward its cooperating brake element to set the brake, releasable power operated mechanism associated with the shiftable pulley mounting for urging the shiftable pulley mounting in a band-tightening direction, releasable power operated mechanism associated With said brake for releasing the brake against bias of said yielding means, and manually-operated control mechanism for said first mentioned releasable power operated mechanism.

3. In a machine of the class described, a fixed supporting structure, a plurality of pulleys, a cutting band trained over said pulleys, means mounting one of said pulleys for shifting movements toward and from the other pulley structure to effect tightening and loosening of the band, a normally set brake associated with the shiftable pulley mounting for arresting band loosening movements of the shiftable pulley, said brake comprising cooperating brake elements, structure mounting one of the brake elements on the fixed supporting structure and the other thereof on the shiftable pulley mounting means and guiding one thereof for movements toward and away from the other thereof, yielding means urging said movable brake element toward its cooperating brake element to set the brake, and a fluid pressure system including a pump, a fluid pressure motor located adjacent the shiftable pulley mounting for urging said shiftable pulley mounting in a band-tightening direction, and a second fluid pressure motor associated with said movable brake element and operative to urge the movable brake element in a brake-releasing direction against bias of said yielding means, said yielding means moving said movable element toward brake setting engagement with its cooperating brake element responsive to release of pressure when the pump is rendered inoper ative.

4. In a machine of the class described, a fixed supporting structure, a plurality of pulleys, a cutting band trained over said pulleys, means mounting one of said pulleys for shifting movements toward and from the other pulley structure to effect tightening and loosening of the band, a normally set brake associated with the shiftable pulley mounted for arresting bandloosening movements of the shiftable pulley, said brake comprising a rack element and a cooperating pawl element, structure mounting one of said elements on the fixed supporting structure and the otherthereof on the shiftable pulley mounting means and guiding said pawl element for movements toward and from the rack element to set and release the shiftable pulley mounting, yielding means biasing the pawl element toward the rack element, and releasable pressure means associated with the brake and with said means mounting the shiftable pulley for urging the shiftable pulley in a direction to tighten said band and for simultaneously urging said pawl element in a direction away from said rack element against bias of said yielding means, said yielding means being responsive to release of said releasable pressure means to move said pawl element toward engagement with said rack element.

5. In a machine of the class described, a fixed supporting structure, a plurality of pulleys, a cutting band trained over said pulleys, means mounting one of said pulleys for shifting movementstoward and from the other pulley structure to effect tightening and loosening of the band, a normally set brake associated with the shiftable pulley mounted for arresting bandloosening movements of the shiftable pulley, said brake comprising a rack element and a cooperating pawl element, structure mounting one of said elements on the fixed supporting structure and the other thereof on the shiftable pulley mounting means and guiding said pawl element for movements toward and from F the rack element to set and release the shifta-ble pulley mounting, yielding means biasing the pawl element toward the rack element, releasable power operated mechanism associated with the shiftable pulley mounting for urging the shiftable pulley mounting in a band-tightening direction, releasable power-operated mechanism associated with said pawl element for moving the pawl element away from said rack element against the action of said yielding means, and manually operated control mechanism for said first mentioned releasable power operated mechanlsm.

6. In a machine of the class described, a fixed supporting structure, a plurality of pulleys, a cutting band trained over said pulleys, means mounting one of said pulleys for shifting movements toward and from the other pulley structure to effect tightening and loosening of the band, a normally set brake associated with the shiftable pulley mounting for arresting bandloosening movements of the shiftable pulley, said brake comprising a rack mounted for common movements with the shiftable pulley mounting and a, pawl, means mounting said pawl on the fixed supporting structure and guiding said pawl for'movements toward andfrom the rack to set and release the shiftable pulley mounting, a spring biasing the pawl toward the rack, and a fluid pressure system including a pump, a fluid pressure motor located adjacent the shiftable pulley mounting for urging said shiftable pulley mounting in a band-tightening direction, a second fluid pressure motor for moving the pawl in a direction away from said rack against bias of said spring, and a common control valve for said motors, said spring moving said pawl toward brake-setting engagement with the rack responsive to release of pressure when the pump is rendered inoperative.

ROBERT L. CRANE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 512,790 Bachman Jan. 16, 1894 1,074,197 Pelton Sept. 30, 1913 2,395,237 Swenson Feb. 19, 1946 

